Novel measurement technique for the electromagnetic characterization of coating materials in the sub-THz frequency range

Abstract

This paper describes a reliable, handy, and inexpensive measurement system to characterize, in the sub-THz frequency range, the coating materials used in the beam pipes of accelerators. The method is based on time domain measurements of an electromagnetic wave passing through a waveguide having a thin central slab, where the coating material is deposited on both sides. Two horn antennas are integrated on both sides of the device to optimize the signal collection and detection. This novel technique is tested on slabs coated with a nonevaporable getter (NEG) and allows to evaluate the surface impedance in the frequency range from 0.1 to 0.3 THz.

Sub-THz Waveguide Spectroscopy of Coating Materials for Particle Accelerators

“…Results agree fairly well both with previous data obtained on different NEG samples using the circular waveguide [16] and DC (direct current) conductivity values extracted using the frequency domain approach [10]. Nevertheless, differently to these latter measurements, a TD method allows to evaluate the electromagnetic properties of coatings in a reliable and simple way exploiting tailored (and reusable) waveguides.…”

“…The THz beam is polarized with its electric field parallel to the waveguide slab. The use of a device having a square cross section marks an improvement in terms of beam collection efficiency with respect to previous measurements [16]. However, compared to the free space signal, the transmitted electric field is in the order of 10% only.…”

“…The design allows us to measure in a simple way large area coating deposited on metallic plates as in the case of accelerators, where averaged quantities are needed. This technique has been successfully used to characterize NEG samples deposited on both sides of thin copper slabs inserted in a circular waveguide [16]. In the case of amorphous carbon however, because of the high temperature growth and the demanding sample thickness requirement, two side deposition is not a feasible approach, because the slab will experience mechanical stress followed by sample peel-off.…”

Multi-Pass Free Electron Laser Assisted Spectral and Imaging Applications in the Terahertz/Far-IR Range Using the Future Superconducting Electron Source BriXSinO

“…The output characteristics are MW range pulse power, pulse durations in the order of picoseconds (10-1,000 optical cycles), up to few GHz of micro pulse repetition rates, and the continuous and fast tuning over a wide range of wavelengths combined with coherent radiation properties. Infrared and THz radiation is of great interest for various applications and for studying fundamental mechanisms [62][63][64][65][66]. Just to name, some examples are: strongly correlating quantum systems, magnetic states in solids, complex fluids, bio-fluids, nanoscopic structures, membrane proteins, bio-molecules, functioning dynamics in biosystems, materials chemistry, electronic transitions in semiconductors, including interband dynamics, phonon scattering and inter-sub band dynamics in quantum wells, inter-sublevel spectroscopy and polaron dynamics in quantum dots, polaron dynamics, coherent dynamics, spin dynamics, impurities in semiconductors, vibrations in crystalline solids and amorphous materials covering the local modes in insulators, vibrational modes of hydrogen-like atoms and molecules.…”